1. Field of the Invention
The invention relates to a control system for a vehicle, which includes two electric motors that are able to output starting torque for starting an engine and, more particularly, to a technique at the time of starting the engine.
2. Description of Related Art
There is known a vehicle that includes a first electric motor (for example, a starter) that is able to output starting torque for starting an engine and a second electric motor (for example, drive motor) that is able to output the starting torque and running torque. This is, for example, a vehicle described in Japanese Patent Application Publication No. 2012-111267 (JP 2012-111267 A) or a vehicle described in Japanese Patent Application Publication No. 2000-154741 (JP 2000-154741 A). JP 2012-111267 A describes that, in a hybrid vehicle that includes a starter for starting an engine and a generator motor having the function of starting the engine and the function of propelling the vehicle by transmitting power to wheels, the reliability of engine starting at a low temperature is improved (that is, the startability of the engine is ensured) by cranking the engine with both the torques with the use of both the starter and the generator motor at the time of starting the engine in a cold state.
Incidentally, in the above-described vehicle, when the engine is started with the use of the drive motor during motor running in which the vehicle travels with the use of only the drive motor, the drive motor needs to output the sum of “running torque+starting torque”. As a result, during motor running, in order to ensure engine starting with the use of the drive motor (in other words, in order to reserve charged electric power of a battery that supplies electric power to the drive motor for engine starting), the amount of running torque is limited (that is, a motor running region is limited; in other words, the electric power of the battery, which is allowed to be used in motor running, is limited). Against such an inconvenience, the vehicle that includes the starter and the drive motor is able to use both in engine starting, so not only the two electric motors are simply used in an engine cold state but also there is still room for improvement in engine starting. The above-described challenge is not publicly known.